Spark gap and discharge control apparatus



Feb. 17, 1970 'r. R. ICONNELL 3,

SPARK GAP AND DISCHARGE CONTROL APPARATUS Filed 001;. 11, 1966 2Sheets-Sheet 1 Ili'l/ FIG. 3

INVENTOR THOMAS R. CONNELL ATTORNEY United States Patent 3,496,409 SPARKGAP AND DISCHARGE CONTROL APPARATUS Thomas R. Connell, Wadsworth, Ohio,assignor to The Ohio Brass Company, Mansfield, Ohio, a corporation ofNew Jersey Filed Oct. 11, 1966, Ser. No. 585,846 Int. Cl. H02h 3/22,9/06 US. Cl. 315-36 10 Claims This invention relates to spark gaps andpreionizing and control devices for lightning arresters and overvoltagedischarge devices and the like.

A principal object of the invention is to provide spark gaps forlightning arresters and overvoltage discharge devices and the likehaving constant breakdown voltages.

Another object of the invention is to improve the operating reliabilityof lightning arresters and the like for switching surges.

Another object of the invention is to provide a spark gap and preionizerarrangement in which the breakdown voltage is within a predeterminedrange of voltages from the design breakdown voltage over a longoperating lifetime.

Another object of the invention is to provide a spark gap and preionizerarrangement in which the effect of production variations in dimensionsof the gap parts and spacing of the gap electrodes on the breakdownvoltage is minimized.

In lightning arresters and the like, it is known to illuminate the maingap by an auxiliary or preionizing gap which serves as a source of ionsfor imparting a conductivity to the atmosphere between the main gaps.The auxiliary gap is arranged to fire at relatively low currentdensities so that the spacing between the electrodes is maintainedwithin close size and dimensional tolerances throughout the life of thearrester. Such arrangements are useful since the auxiliary gap is not inthe main discharge path of the arrester and may be designed andconstructed with precise parts and manufactured to within closetolerances and at relatively low cost. This result could not be achievedeconomically by design of the main gap.

However, the problem is of some complexity since, in order to achieveproper operation, it is necessary to insure response of the auxiliarygap to excess voltages in the circuit to which the arrester is connectedand to insure operation of the main gap after the auxiliary gap isfired. Further, it is necessary to provide the electrical functioning alimited space and in the proper relation to the main gap of thearrester.

The present invention relates to a spark gap and a discharge control andpreionizing apparatus, in which a novel arrangement of auxiliaryswitching gaps and voltage grading means is associated with the maingaps of the lightning arrester. The main gaps, auxiliary gaps, andgrading means are arranged in a plurality of stages for cascadeoperation in which a first main gap is fired and then the other maingaps are fired in a sequence determined by the upset of voltage divisionbetween the various stages produced by the firing of the switching maingaps. Novel structural arrangements are provided for incorporating themain gaps, auxiliary gaps, and grading devices in a compact unitaryassembly in a lightning arrester.

The invention, together with further objects, features, and advantagesthereof, will be understood from the following detailed specificationand claims and the appended drawings, in which:

FIG. 1 is a side elevation view of a spark gap apparatus embodying theinvention;

FIG. 2 is a schematic diagram showing an overvoltage discharge circuitembodying the novel gap and discharge control and preionizing circuit;

FIG, 3 is a plan view of a gap plate, taken along the line 3-3 in FIG. 1and showing the arrangement of electrodes and grading resistors on thegap plates;

FIG. 4 is a section view of the gap plate of FIG. 3, taken in thedirection 4-4 in FIG. 3; and

FIG. 5 is a schematic diagram of a spark gap embodying an alternativearrangement of a discharge control circuit.

Referring to FIG. 1, there is shown the physical construction of thespark gap 10, in which a plurality of gap plates 11, 12, 13, and 14cooperate with associated center plates 15 and 16 t0 define spark gaps,associated arc chambers, and control and discharge circuits of the gapcontrol stages S1, S2, S3, and S4 of FIG. 2. The plates 11, 12, 13, and14 cooperate with associated center plates 15 and 16 along peripheralridge and recess means and interengage the end faces of a plate member17 which carries a magnetic coil 18 at the center position of the fourgap plates, The entire assemblage is arranged in the form of a stack,and the elements are connected in series with two end plates 19 and 20which function to connect the gap assembly to the terminals of thearrester housing, to the line conductor, and to the valve resistor, asthe case may be.

Referring now to FIG. 2, the spark gap apparatus 10 comprises four maingaps 21, 22, 23, and 24 connected in series and having certainassociated gaps, resistors, and capacitors connected in paralleltherewith to constitute four switching control stages, referred togenerally as S1, S2, S3, and S4, all connected in series with a coil 25associated with the gaps 21 to 24. The apparatus 10 is connected inseries circuit 26 which includes a nonlinear valve resistor 27, apowerline conductor 28, and a ground 29, and constitutes a protectivecircuit or lightning arrester for the powerline 28.

The coil 25 comprises a means for generating a magnetic field toelongate the arcs in the several gaps 21 to 24. Two fixed gaps 30 and 31are connected in shunt with the coil 25 and function during initialdischarge of energy from the line 28 to the ground 29 through the gaps21 to 24. After a sufficient time interval, current flow, in the coil 25extinguishes the arcs in the gaps 30 and 31 so that an increasingmagnetic field is generated by the coil for moving the arcs in the gaps21 to 24. The gaps 30 and 31 may be replaced by arrangements ofnonlinear resistors, as is described in US. Patents 2,825,008 and3,019,367 to I, W. Kalb, or by arrangements of arc elongatingelectrodes, within the contemplation of the invention.

In the apparatus 10, the gap control stage S1 is constituted by the gap21, a switching gap 32 having series connected switching resistors 33and 34, and a grading resistor 35. Gap control stage S2 comprises thegap 22, a switching gap 36 with series switching resistors 37 and 38,and a grading resistor 39. The gap control stage S3 comprises the gap23, a grading capacitor 40, and a grading resistor 41. The gap controlstage S4 comprises a switching gap 42 with series resistors 43 and 44,and a grading resistor 45. The described parts are connected in aparallel circuit to constitute the designated stage.

The stages S1, S2, and S4 have the same grading resistances, that is,the grading resistors 35, 39, and 45 are equal, whereas the resistanceof the grading resistor 41 of stage S3 is small relative to resistors35, 39, and 45. The switching gaps 32, 36, and 42 are designed andadjusted to sparkover at substantially the same voltage, less than thebreakdown voltage of the mains gaps, but the associated seriesresistors, that is, the resistors 33 and 34 of the gap 32, the resistors37 and 38 of the gap 36, and the resistors 43 and 44 of the gap 42, areprogressively smaller for the successive stages so that an unequalvoltage division exists as between the main gaps 21, 22, and 24 afterthe switching gaps have fired.

The switching gaps 32, 36, and 42 are small gaps having preciselydimensioned electrodes positioned adjacent the main gaps 21, 22, and 24.The switching gaps function as preionizers for the main gaps as well asa switching means for the several switching stages, and are adapted fordischarge in a narrow, predetermined range of voltages over the range ofdesign tolerances. In production, one of the gaps 32, 36, and 42 isselected to spark over at a voltage close to the design voltage, andminor production variations in the remaining switching gaps do notmaterially alter the overall functioning, inasmuch as the gap 32determines the firing sequence of the stages because of the largervalues of resistors 33 and 34.

The functioning of the apparatus is dependent upon the nature of theovervoltage on the conductor 28. The functioning for line overvoltageswhich have slowly rising wave fronts or switching surge voltages, socalled, is as follows:

The line voltages are divided between the several main gaps 21 to 24 inthe same proportions as the resistance of the individual gradingresistors 35, 39, 41, and 45 to the total grading resistance constitutedby the four resistors. Accordingly, with the grading resistancesheretofore described and, prior to discharge of the switching gap 32,the line voltage is divided with equal voltages across stages S1, S2,and S4 and a much lesser voltage across S3.

Upon the occurrence of an overvoltage on line conductor 28, theswitching gaps 32, 36, and 42 spark over and connect the switchingresistors 33 and 34 in parallel with the grading resistors 35, theswitching resistors 37 and 38 in parallel with the resistor 39, and theswitching resistors 43 and 44 in parallel with the grading resistor 45.The resistors 33 and 34 are substantially larger than the resistors 37and 38, which are in turn substantially larger than resistors 43 and 44.Accordingly, after the switching gaps 32, 36, and 42 have fired, thedistribution of line voltage as between the stages S1, S2 and S4 isaltered so that a greater proportion of the line voltage appears acrossthe gaps 21, 22, and 24, in that order, in accordance with theinequality between the parallel resistances of the stages S1, S2, andS4. Accordingly, the gap 21 fires first, followed by the gap 22 and thegap 24, whereupon all the line voltage appears across the gap 23 whichis fired last. This completes the firing sequence and initiates thedischarge sequence in which transient energy is discharged from the lineconductor 28 to the ground 29, through the valve resistor 27. In thedischarge sequence, the coil functions to elongate the arcs of the maingaps 21 to 24 to terminate the discharge, all as described in thepatents heretobefore referred to.

The resistor 41 is chosen so that its resistance is less than theparallel grading and switching gap resistances of the stages S1, S2, andS4 with the switching gaps fired, so that the main gap 23 is fired onlyafter the main gap firing sequence, gap 21, gap 22, gap 24, iscompleted. Resistor 41 is small in relation to the individual gradingresistances 35, 39, and 45, which insures that the switching gaps 32,36, and 42 are fired before the main gap 23 is fired.

The functioning of the discharge control circuit for line overvoltageswhich have rapidly rising wave fronts, impulse voltages so-called, is asfollows:

The impulse voltages are divided between the several main gaps inproportion to the impedance of a given stage, as the impedance of thecapacitor 40, or the com bined impedances of the capacitor and thegrading resistor 41, for the stage S3 or the resistance of the gradingresistors 35, 39, and 45 for the stages S1, S2, and S4 to the seriesimpedance of the combined stages. The capacitor 40 has a capacitancewhich is large in comparison with the distributed capacitances acrossthe stages S1, S2, and S4, so that, for impulsive voltages having asufiiciently high rate of increase, the proportional impedance of thestage is low and the impressed voltage is divided substantially betweenthe main gaps 21, 22, and 24. Accordingly, the main gaps 21, 22, and 24fire, although not necessarily in that order, whereupon the impressedvoltage is applied directly across the stage S3 to fire the main gaps23.

The firing sequence just described is dependent primarily upon thevoltage upset between the stages produced by the fast wave frontimpulses applied to the grading capacitor 40 and is not substantiallydetermined by the functioning of the switching gaps. The firing order asbetween the main gaps 21, 22, and 24 will, generally speaking, beindeterminate rather than determined as to the gap 21 by the firing ofthe switching gap 32.

In both embodiments of the invention, th voltage at which the switchinggaps lose control of main gaps, that is, cease to determine the firingorder, is dependent primarily upon the rate of rise of the impulsevoltage, and the control function may be retained for faster impulses byequalizing the time constants of the stages.

Referring now FIG. 3 and FIG. 4, the construction of the stage S4 of theapparatus 10 is illustrated by the construction of the gap plate 14. Theplate 14 comprises a circular plate formed of arc resistant ceramicmaterial and having a circumferential ridge 50 and an interior surface51 of the plate defining an arc chamber 52. Two main gap electrodes 53and 54, comprising the main gap 24, are carried by the plate 14 andsecured thereto and to the plate 16 by means such as epoxy adhesives andassociated rivets 55 and 56. Two ceramic barrier members 57 and 58integral with the plate 14 define the extremities of the arc chamber 52and the limit of elongating arc movement from the adjoining arcing facesof the electrodes 53 and 54 along the diverging extremities thereof andtoward the radially outward extremities of the are chamber under theinfluence of the magnetic field generated by the coil 18.

A separate member 60 formed of ceramic material is secured to thesurface of the plate 14 between the mem bers 57 and 58. The member 60supports two electrodes 61 and 62 which constitute the switching gap 42and have the bodies formed of resistive material to constitute theswitching resistors 43 and 44. The electrodes 61 and 62 are formed ascylindrical bodies of resistive material which are received incylindrical openings in elevated portions of the member 60 and have theinterior ends closely spaced at a predetermined distance to constitutethe gap 42. A resistor 63 is disposed between the radially outwardextremity of the member 60 and the peripheral rim 50 of the plate 14 andconstitutes the grading resistor 45 of FIG. 1. The lead wires of theresistor 63 are connected to the electrodes 61 and 62 and to theelectrodes 53 and 54 to constitute the parallel circuit arrangement ofstage S4.

The gap plates 11, 12, and 13, comprising the stages S1, S2, and S3, maybe constructed in the same way as the stage S4, just described. Thestage S3 may be constituted by substituting a resistor corresponding tothe resistor 41 for the two electrodes 61 and 62 and a capacitorcorresponding to the capacitor 40 for the resistor 63 or, conversely,substituting the resistor 41 for the resistor 63 and the capacitor 40for the electrodes 61 and 62.

In the embodiment of FIG. 2, selection of main gaps for critical spacingis important only for the main gap 21 and the remaining gaps 22, 23, and24 are relatively tolerant of production variations in spacing.

The spark gap apparatus 65 of FIG. 5 comprises an arrangement of maingaps and a discharge control and preionizing circuit in four stages S5,S6, S7, and S8, gen erally similar in construction and functioning tothe spark gap and discharge control apparatus of FIG. 1 and FIG. 2.However, the apparatus 65 incorporates a symmetric arrangement of stagesS6 and S7 with respect to the stages S5 and S8 so that the gap plateassembly 11, 15, 12 is identical with the gap plate assembly 13, 16, 14.

As shown in FIG. 5, the *rnain gaps 66, 67, 68, and 69 are connected inparallel with associated grading resis tors 70, 71, 72, and 73 andassociated switching gap 74, grading capacitor 75, grading capacitor 6,and switching gap 7 to constitute the stages S5, S6, S7, 'and S8,respectively. The several stages are connected in series with each otherand with a magnetic coil 78 having parallel connected gaps 79 and 80, asin the apparatus 10 of FIG. 1. p

The grading resistances 70 and 73 are equal and the grading resistances71 and 82 are equal, with the resistances 70 and 73 much larger than theresistances 71 and 72. Accordingly, line voltages and transientovervoltages impressed on the apparatus 65 are divided unequally betweenthe main gaps 66 and 69 and main gaps 67 and 68. The resistors connectedin series with the switching gaps 74 and 77 are unequal, the resistorsof the gap 74 being larger than ,the resistors of the gap 77 so that atransient overvoltage fires both of the switching gaps 74 and 77, whichin turn causes the main gap 66 to fire and then the main gap 69. Withgaps 66 and 69 conducting, the entire line voltage is impressed upon themain gaps 67 and 68 which causes them to fire. The gaps 67 and 68 firesimultaneously if resistors 71 and 72 are equal. If resistors 71 and 72are unequal, as in a preferred embodiment hereof resistor 71 is l megohmand resistor 72 is 2 megohms, the gaps 76 and 75 fire in that order. Ingeneral, inequality of the grading resistors 71 and 72 equalizes thetime constants of the two stages S6 and S7.

The functioning of the apparatus 65 for overvoltages with rapidly risingwave fronts is such that the grading capacitors 75 and 76 impress asubstantial proportion of the line voltage across the main gaps 66 and69 and the associated switching gaps 74 and 77. Accordingly, these gapsare fired, and the line voltage is then impressed across the main gaps67 and 68 which are fired to initiate the discharge sequence. Thecapacitances of the capacitors 75 and 76 may be in the order of 20 timesthe distributed capacitance, in practical devices, to impress more than90 percent of the line voltage across the stages S5 and S8. Accordingly,the embodiment of FIG. 5 produces improved sparkover performance forimpulse voltages as well as for switching surges.

The capacitors 75 and 76 may be made unequal and/or the gradingresistors 71 and 72 may be made unequal to determine a voltage upset andpreferential firing order of the stages S6 and S7 A lightning arresterutilizing the circuit arrangement of FIG. 2 as a gap control andembodying the features of US. Patents 2,825,008 and 3,019,367, andfeatures of copending applications 624,275 filed Mar. 20, 1967, and598,467, filed Dec. 1, 1966, used the following values:

Grading resistorsR35, R39, R45, 15 megohms; R41, 0.5 megohm.

Switching resistors and switching gapG32, R33, R34, 10 megohms.

Switching gap fired-G36, R37, R38, 6 megohms; G42, R43, R44, 1 megohm.

Grading capacitorC40, 100 mmfd.

The apparatus, including spark gaps and magnetic coil, were incorporatedin the gap assembly of FIG. 1 and utilized at a nominal operatingvoltage of 4.5 kilovolts. Tests demonstrated consistent sparkoverperformance for long duration surges and for impulse voltages.

The arrangement of the above described embodiments, inwhich theresistance of the series combination of switching gap and two switchingresistors, when the switching gap is fired, is less than the resistanceof the associated grading resistor, is preferred to arrangements inwhich the resistance of the switching gap and switching resistors isgreater than the resistance of the associated grading resistor.

One advantage of the spark gap arrangements described herein, andparticularly of the embodiment of FIG. 5, is

that very high values of grading resistances may be utilized fordetermining the initial voltage distribution between the stages, or maybe omitted entirely without affecting the order in which the main gapsare fired. Thus, in one embodiment of the apparatus of FIG. 5, theresistors 70 and 73 were omitted entirely and the remaining componentshad the following values:

Grading resistors-R71, 0.5 megohm; R72, 1.0 megohm.

Switching resistors and switching gap-G74, 8.5 megohms.

Switching gap firedG77, 4.5 megohms.

Grading capacitors-C75, 200 mmfd.; C76, mmfd.

Tests demonstrated consistent sparkover characteristics for longduration surges and for impulse voltages. In another embodiment of theapparatus of FIG. 5, the grading resistors R70 and R73 are each 15megohms, and the other components having the same magnitudes.

One feature of the new spark gap apparatus is that a much larger gapelectrode spacing may be utilized for a given breakdown voltage whilemaintaining a consistent sparkover function. Increase in gap spacingreduces the effect of variations in dimensions of the gap electrodes.

The term time spectrum is used to refer to the range of rise times or ofdelay times of the impressed wave of overvoltage or both.

It is to be understood that the foregoing description is not intended torestrict the scope of the invention and that various rearrangements ofthe parts and modifications of the design may be resorted to. Thefollowing claims are directed to combinations of elements which embodythe invention or inventions of this application.

I claim:

1. Spark gap and discharge control apparatus comprising a plurality ofgap electrodes and grading means therefor, said gap electrodes andgrading means constituted as a plurality of stages of parallel connectedelements in series connection, stage by stage, each stage comprising twoelectrodes constituting a main gap, a first resistive grading means inparallel with the main gap, the said first resistive grading means ofthe said several stages dividing voltages between the stages, and aswitching gap and series switching resistor connected in parallel withthe main gap, the switching gap of each stage having electrodespositioned adjacent the associated main gap electrodes and communicatingwith the main gap to constitute a preionizer therefor, the resistance ofthe series switching resistor and switching gap being unequal in theseveral stages to constitute a second voltage grading means forpreferentially firing the main gap of one of the stages prior to themain gaps of the remaining stages.

2. Spark gap and discharge control apparatus in accordance with claim 1,in which the resistance of the series switching resistor and switchinggap of the said one stage is greater than the resistance of the seriesswitching resistor and switching gap of each of the remaining stages andis less than the resistance of the first resistive grading means of thesaid one stage, all for predetermining the preferential firing of themain gap of the said one stage independent of firing sequence of theswitching gaps.

3. Spark gap and discharge control apparatus in accordance with claim 2,in which the main gap of the said one stage is critically spaced topredetermine the breakdown voltage thereof, the remaining main gapsbeing relatively independent of small variations in the spacing of theelectrodes thereof.

4. Spark gap and discharge control apparatus comprising a plurality ofgap electrodes and grading means therefor, said gap electrodes andgrading means constituted as a plurality of stages of parallel connectedelements in series connection, stage by stage, each stage comprising twoelectrodes constituting a main gap, a first resistive grading means inparallel with the main gap in each of the stages, the said firstresistive grading means of the said several stages dividing voltagesbetween the stages, a

switching gap and series switching resistors connected in parallel withthe main gap in at least one of the stages, the switching gap havingelectrodes positioned adjacent the main gap electrodes and communicatingtherewith to constitute a preionizer, all for firing the main gap inresponse to overvoltages having slow wave fronts, and capacitive gradingmeans connected in parallel with the main gap in at least one of thestages for firing the main gaps of the remaining stages in response toovervoltages having fast wave fronts, and all providing predeterminedfiring sequences of the main gaps for a wide time spectrum ofovervoltages.

5. Spark gap and discharge control apparatus in accordance with claim 4,in which there are four gap stages connected in series and comprisingthree stages, similar to the described one stage, having switching gapelectrodes connected in parallel with the main gap electrodes thereof,and one stage having a capacitor connected in parallel with the main gapthereof.

6. Spark gap and discharge control apparatus in accordance with claim 4,in which there are four gap stages connected in series and comprisingtwo stages having switching gap electrodes connected in parallel withthe main gap electrodes thereof, and two stages having capacitorsconnected in parallel with the main gap electrodes thereof.

7. Spark gap and discharge control apparatus in accordance with claim 4,in which there are two stages having switching gaps and switchingresistances in parallel with the main gaps thereof and at least onestage having a capacitor connected in parallel with the main gapthereof, and the first-named two stages have equal time constants forcontrol of the main gaps in response to overvoltages having fast wavefronts.

8. Spark gap and discharge control apparatus comprising a plurality ofgap plates and a magnetic coil in stacked arrangement and a plurality ofgap electrodes and grading means carried by the said gap plates, thesaid gap electrodes and grading means constituted as a plurality ofstages of parallel connected elements in series connection, stage bystage, and in series with the magnetic coil, each stage comprising twoelectrodes constituting a main gap having electrodes with divergent arcfaces positioned in the field of the magnetic coil, a first resistivegrading means in parallel with the main gap, the said first resistivegrading means of the several stages dividing voltages between thestages, a switching gap and series switching resistors connected inparallel with the main gap in at least one of the stages for upsettingthe voltage division produced by the first grading means, the switchinggap having a breakdown voltage less than the breakdown voltage of themain gap and having electrodes positioned adjacent the main gapelectrodes and communicating therewith to constitute a preionizer, allfor firing the main gap in response to overvoltages having slow wavefronts, and capacitive grading means connected in parallel with the maingap for firing the main gaps of the remaining stages in response toovervoltages having fast wave fronts, and all providing a predeterminedfiring sequence of the said main gaps and initiating current flow in themagnetic coil.

9. Spark gap and discharge control apparatus in accordance with claim 8,in which the switching gap electrodes comprise cylindrical members ofresistive material constituting the series switching resistors, andmeans supporting the switching gap electrodes in spaced relationadjacent the electrodes of the main gap.

10. Spark gap and discharge control apparatus in accordance with claim9, in which the main gap electrodes are carried by a gap plate, and themeans supporting the switching gap electrodes is carried by the gapplate.

References Cited UNITED STATES PATENTS 2,623,197 12/1952 Kalb 315-362,825,008 2/1958 Kalb 315-36 X 3,076,114 1/1963 Hicks 315-36X 3,377,5034/1968 Osterhout 315-36 JOHN W. HUCKERT, Primary Examiner I. R.SHEWMAKER, Assistant Examiner U.S. Cl. X.R. 313-326

1. SPARK GAP AND DISCHARGE CONTROL APPARATUS COMPRISING A PLURALITY OFGAP ELECTRODES AND GRADING MEANS THEREFOR, SAID GAP ELECTRODES ANDGRADING MEANS CONSTITUTED AS A PLURALITY OF STAGES OF PARALLEL CONNECTEDELEMENTS IN SERIES CONNECTION, STAGES BY STAGE, EACH STAGE COMPRISINGTWO ELECTRODES CONSTITUTING A MAIN GAP, A FIRST RESISTIVE GRADING MEANSIN PARALLEL WITH THE MAIN GAP, THE SAID FIRST RESISTIVE GRADING MEANS OFTHE SAID SEVERAL STAGES DIVIDING VOLTAGES BETWEEN THE STAGES, AND ASWITCHING GAP AND SERIES SWITCHING RESISTOR CONNECTED IN PARALLEL WITHTHE MAIN GAP, THE SWITCHING GAP OF EACH STAGE HAVING ELECTRODESPOSITIONED ADJACENT THE ASSOCIATED MAIN GAP ELECTRODES AND COMMUNICATINGWITH THE MAIN GAP TO CONSTITUTE A PREIONIZER THERE-